A portion of the disclosure of this patent document contains material which is subject to copyright protection, such as illustrations of computer generated characters. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
1. Field
This application relates generally to computer graphics, and more specifically to the deformation of skin on a computer generated character in computer animation.
2. Related Art
In the field of computer animation, a computer generated character is typically modeled using a skeleton structure that is covered with a skin layer. An artist may achieve the visual effect of animation through movements of the bones and joints in the skeleton structure. The skin layer covering the skeleton structure moves, or deforms, in response to movements of the skeleton structure and imparts a visually plausible appearance to the computer generated character. The use of a skeleton structure and skin deformation to animate a computer generated character is more computationally efficient than the use of, for example, multiple individual drawings to produce animation.
Since the skin layer of a computer generated character is outwardly visible to viewers of the computer animation, an efficient deformation technique that produces convincing skin deformations is desirable. For example, if an artist chooses to bend the elbow of a computer generated character, it would be desirable to deform the skin layer with a life-like bulge at the bicep with minimal input from the artist and by using minimal computing resources.
Conventional deformation techniques are by artists to produce skin deformations. A conventional deformation technique may, however, require significant input from an artist before it becomes configured to produce skin deformations. For example, a conventional deformation technique known as skeleton subspace deformation (SSD) requires an artist to identify and to assign numerical weights to portions of a skeleton structure prior to skin deformation. The process of assigning multiple numerical weights to skeletal portions (e.g., skin vertices), called “weight painting,” is time-consuming, especially for skin areas of a computer animated character that exhibit frequent and/or complex movements.
In addition, an artist may perform weight-painting for a conventional deformation technique only to find that the conventional deformation technique produces a visually unconvincing skin deformation. For example, a conventional deformation technique, including SSD, may produce a skin deformation that shows crunching or shrinkage of skin around a bent elbow, as illustrated in FIGS. 2A and 2B, respectively. Notably, an artist may have to re-perform the weight painting process in order to improve upon the visually unconvincing deformation. Further, the artist may resort to deforming multiple skin layers between a skeleton structure and a final skin to improve upon the deformation. Further yet, the artist may perform the deformation process anew using another conventional deformation technique. These options are time-consuming and/or computationally expensive.
A conventional deformation technique may also fail to provide artist controls for enhancing the realism of a skin deformation. For example, a conventional deformation technique may fail to produce sufficient bulging of the bicep in response to a bent elbow. In order to introduce bulging into a skin layer, an artist using a conventional deformation technique may introduce volume constraints (e.g., limits) that disallow the deformation of skin into a defined volume during the deformation process. However, the introduction of volume constraints is time-consuming for the artist and/or computationally expensive.